photo source: www.geneplanet.com
Sunscreens are for topical preparations containing substances that partially or completely block light radiation. They appeared in the 1940s for photoprotection of American soldiers in the Pacific during World War II, since then its use has spread universally.
They are classified into two groups: partial or total chemical and or physical. The degree of protection from attempts to quantify a filter through so-called sun protection factor (SPF), or simply more protection index (PI). It is expressed with a numeric index ranging from 4 to maximum of 35 or more.
The SPF means the ratio of mean dose obtained in erythema skin covered with the filter and the average dose of the same skin erythema without protection measures both in the laboratory with the same light source and the same focus-skin distance. In a medium dose skin erythema which is 20 minutes if you apply a filter SPF 10 increases its resistance to 200 minutes.
A solar filter must meet the following conditions must be sufficiently adherent to the skin to resist once the moisture from perspiration and immersion in water should be safe and cosmetically acceptable and must express your FPS in the container, valued even by separately for UVB and UVA.
Sunscreens are essential today, but must take care that their use is correct to reject the idea that by using a protective filter can stay many hours in the sun. The SPF number indicates it is not always accurate, sometimes falling below the theoretical. Users tend to apply them in smaller quantities without properly extend through the skin in quantity and size. Should apply not only sufficient but also a uniform and consistent across the surface of exposed skin. Frequency of application will be after every dive even though the filter presumed to be resistant to water and regularly if for professional or sporting imperative need to stay longer under the sun exposure. It should use a sunscreen suitable for every skin type. For fair skin and for children is recommended SPF 35 or higher, in brown skin can be enough FPS between 20 and 25.
Ultimately the best photoprotection is once recognized the characteristics of the skin, not to abuse the exposure time even using sunscreen.
Source: http://www.cancerpiel.com/proteccion.htm
Tags: filter system of skin, protection index, skin filter system, skin protection, sun protection factor, sunscreens
